A structure 1 comprises, from its rear side to its front side, a carrier substrate 4, an insulating layer 3, and a useful layer 2, with the useful layer 2 having a free surface S. In a method for processing such a structure 1 known from the state of the art, and illustrated in FIGS. 1 and 2, the structure 1 is placed in an atmosphere comprising chemical species in a gaseous form 6, with the chemical species 6 being likely to chemically react with the useful layer 2, with kinetics strictly increasing with the temperature of the useful layer 2.
During the treatment process, the structure 1 is held on a support structure 5 (or “chuck”). The structure support 5 is positioned in a reaction chamber 9.
The useful layer 2 is generally uniformly heated using a heating system 7, for example, heating resistors or still halogen lamps.
The chemical species 6 injected into the reaction chamber 9 thus chemically react with the free surface S of the useful layer 2. The type of chemical reaction depends on the nature of the chemical species 6 and on the useful layer 2, and may then take the form of a thinning by etching of the useful layer 2, or thickening by epitaxy of the useful layer 2.
However, the useful layer 2 generally has variations in thickness and the methods for etching or thickening by epitaxy are known to be non-uniform and even increasing a bit more the variations in thickness of the useful layer 2. Variations in the thickness of the useful layer 2 thus remain after the treatment process.
Therefore, the main disadvantage of such treatment method is that, during the thinning or thickening reaction, the variations in thickness of the useful layer 2 remain and may even be increased.
The structures 1, such as the structures of the semiconductor-on-insulator (SeOI) type thus have variations in thickness, the spectral analysis of which reveals components having spatial wavelengths varying from a few nanometers (roughness-like) to the size of the structure 1 (non-uniformity-like). Some techniques (smoothing annealing in a reducing atmosphere, for example) make it possible to reduce the variations in spatial wavelength thickness below a certain threshold, for example, 2 μm. However, over the range of spatial wavelengths beyond such threshold, for example, from 2 μm to a few centimeters, reducing the non-uniformities in the thickness of the useful layer 2 remains very difficult.
In particular, a method for thickening the semiconductor layer by epitaxy, or for thinning the semiconductor layer by etching, in a structure 1 of the SeOI type, does not significantly reduce the variations in thickness of the semiconductor layer on an extensive range of wavelengths.
The disclosure, therefore, provides a method for treating a structure 1 aiming at reducing the variations in thickness of the useful layer 2.